176 Dr Johannes Walther-The North American Deserts.
is able to detach and sweep down a much larger amount of
debris which afterward the Colorado carries out into the gulf of
California.
Thus we see in the canyon of the Colorado an interesting ex
ample of the combined action of erosion and deflation. We
recognize in the inner gorge a simple channel of erosion; we ob
serve that the upper amphitheaters owe their existence to the
cooperation of erosion and deflation.
Now, what we here see in the Colorado, that we see every
where on earth where the soil is not covered by a mantle of
water, snow or vegetation. There is no need of traveling into
the deserts in order to recognize the denuding activity of wind;
and in the driest desert the traces of erosion may be observed.
There is no region absolutely devoid of precipitation, and, on
the other hand, deflation may be observed in the rainiest climate.
When on a dry autumn day you walk along the highway and
are annoyed by whirling clouds of dust, you are witnessing the
denuding effect of wind. Every sand dune is the result of the
same force. Every clay bed (" Lehmlager ") teaches how vast
deposits are produced by wind, and the loess beds of China are
supposed to be merely a product of deflation. We say of the
wind that it "sweeps " over the ground; for this word means
nothing else than that the wind cleans the ground of all loose
particles that cover it. Translated into technical geologic lan
guage, it is called " deflation," but that means nothing else than
the every-day word "sweep."
One must learn to recognize the sweeping activity of the wind
not only in the desert but everywhere, and in so doing to de
tect in its very beginning the process whose final product von
Richthofen sees in the loess.